Synthesis, characterization and X-ray crystal structure of copper(I) complexes of the 2-(2-quinolyl)benzothiazole ligand. Electrochemical and antibacterial studies

Article abstract of DOI:10.1016/j.poly.2015.05.026

Two new copper(I) complexes of the general formula [Cu(qbtz)(PPh₃)(X)] {qbtz = 2-(2-quinolyl)benzothiazole and X = Br (1), I (2)} have been synthesized and characterized by elemental analyses, IR, UV-Vis and ¹H NMR spectroscopy. The crystal and molecular structures of these complexes have been determined by single-crystal X-ray diffraction. The coordination geometry around the central metal ion is a distorted tetrahedron. The electrochemical behavior of the ligand and its copper(I) complexes has been investigated by cyclic voltammetry in DMF solution. The redox potential of the copper center is influenced by the nature (the σ-donor ability) of the coordinated halide X^-, and it shifts to more anodic potentials for complex 2 as compared to that of 1. The in vitro antibacterial activities of the ligand and its copper complexes were tested against Staphylococcus aureus, Bacillus cereus and Salmonella typhi.

Full text of DOI:10.1016/j.poly.2015.05.026

Accepted Manuscript
Synthesis, characterization and X-ray crystal structure of copper(I) complexes
of the 2-(2-quinolyl)benzothiazole ligand. Electrochemical and antibacterial
studies
Soraia Meghdadi, Mehdi Amirnasr, Afsaneh Mirhashemi, Ahmad Amiri
PII:
S0277-5387(15)00268-5
DOI:
http://dx.doi.org/10.1016/j.poly.2015.05.026
POLY 11325
Reference:
Polyhedron
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Accepted Date:
7 December 2014
13 May 2015
Please cite this article as: S. Meghdadi, M. Amirnasr, A. Mirhashemi, A. Amiri, Synthesis, characterization and X-
ray crystal structure of copper(I) complexes of the 2-(2-quinolyl)benzothiazole ligand. Electrochemical and
antibacterial studies, Polyhedron (2015), doi: http://dx.doi.org/10.1016/j.poly.2015.05.026
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Synthesis, characterization and X-ray crystal structure of copper(I)
complexes of the 2-(2-quinolyl)benzothiazole ligand.
Electrochemical and antibacterial studies
Soraia Meghdadia,*, Mehdi Amirnasra,*, Afsaneh Mirhashemia, Ahmad Amirib
aDepartment of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Iran
bSchool of Chemistry, College of Science, University of Tehran, Tehran, 14155-6455, Iran
Corresponding authors. Tel.: +98-31-3391-2351; fax.:+98-31-3391-2350.
*E-mail address: amirnasr@cc.iut.ac.ir (M. Amirnasr)
smeghdad@cc.iut.ac.ir(S. Meghdadi)
Abstract
Two new copper(I) complexes of the general formula [Cu(qbtz)(PPh3)(X)] {qbtz = 2-(2-
quinolyl)benzothiazole and X = Br (1), I (2)} have been synthesized and characterized by
elemental analyses, IR, UV–Vis and 1H NMR spectroscopy. The crystal and molecular structures
of these complexes have been determined by single-crystal X-ray diffraction. The coordination
geometry around the central metal ion is a distorted tetrahedron. The electrochemical behavior of
the ligand and its copper(I) complexes has been investigated by cyclic voltammetry in DMF
solution. The redox potential of the copper center is influenced by the nature (the σ-donor
ability) of the coordinated halide X−, and it shifts to more anodic potentials for complex 2 as
compared to that of 1. The in vitro antibacterial activities of the ligand and its copper complexes
were tested against Staphylococcus Aureus, Bacillus cereus and Salmonella typhi.
Keywords: 2-(2-quinolyl)benzothiazole; Copper(I) complexes; Crystal structure; Cyclic
voltammetry; Antibacterial activity
1

1. Introduction
Copper(I), with a d10 electronic configuration, is well known for its tetrahedral coordination
geometry and the wide range of applications of its complexes. Many efforts have been made to
design and synthesize new multidentate ligands that are able to control the crystal structure and
properties of copper(I) complexes [1-4]. Through careful choice of the ligand topology, copper(I)
centers can be used for the template directed synthesis of catenanes, rotaxanes and knots [5,6].
Copper(I) complexes of diimine ligands exhibit diverse structures, together with rich
photophysical and redox properties [7-10], and have found important applications in
bioinorganic chemistry [5,6] and the preparation of functional materials [11-13].
2-Substituted benzothiazoles have attracted considerable interest due to their diverse
biological and pharmaceutical properties, such as antiulcer and antihelminthic[14],
antihypertensive [15], anticoagulant [16], antiallergic [17], analgesic [18], anti-inflammatory
[19], antimicrobial [20], antivirial [21], antiparasitic [22], anticancer [23] and enzyme inhibitory
activity [24]. The increasing applications of metal complexes of 2-substituted benzothiazoles,
capable of forming multifunctional complexes, in the area of optoelectronics, the synthesis of
fluorogenic enzyme substrates and fluorescent materials are also well recognized [25-27].
In continuation of our studies on the synthesis of 2-substituted benzothiazoles [28], we wish
to report the synthesis of 2-(quinoline)benzothiazole, under benign and mild reaction conditions
using triphenylphosphite in the simple ionic liquid tetrabutyl-ammonium bromide (TBAB) as the
reaction medium, and its copper(I) complexes [Cu(qbtz)(PPh3)Br] and [Cu(qbtz)(PPh3)I]. The X-
ray crystal structures of both complexes are reported and their cyclic voltammetric behavior and
preliminary antibacterial activity are also discussed.
2

2. Experimental
2.1. Materials and general methods
All solvents and chemicals were of commercial reagent grade and used as received from
Aldrich and Merck. Elemental analyses were performed using a Perkin-Elmer 2400II CHNS-O
elemental analyzer. UV-Vis spectra were recorded on a JASCO V-570 spectrophotometer.
Infrared spectra (KBr pellets) were obtained on a FT-IR JASCO 680 plus spectrophotometer. 1H-
NMR spectra were measured with a Bruker AVANCE III 400 spectrometer (400 MHz). Proton
chemical shifts are reported in parts per million (ppm) relative to an internal standard of Me4Si.
Cyclic voltammograms were recorded using a SAMA 500 Research Analyzer. Three electrodes
were utilized in this system, a glassy carbon working electrode, a platinum disk auxiliary
electrode and Ag wire as a reference electrode. The glassy carbon working electrode (Metrohm
6.1204.110) with a 2.0 0.1 mm diameter was manually cleaned with 1 µm alumina polish prior
to each scan. Tetrabutylammonium hexafluorophosphate (TBAH) was used as the supporting
electrolyte. The solutions were deoxygenated by purging with Ar for 5 min. All electrochemical
potentials were calibrated versus an internal Fc+/o (Eº = 0.40 V vs. SCE) couple under the same
conditions [29].
2.2. Synthesis of the ligand, qbtz
The ligand was prepared according to a procedure reported elsewhere [28]. The synthetic
approach was initiated using a mixture of quinaldic acid and 2-aminothiophenol with
triphenylphosphite in the presence of the inexpensive ionic liquid tetrabutylammonium bromide
(TBAB) at 120 °C. The reaction was completed in 15 min. The final viscous slurry was treated
3

with methanol and the resulting solid was filtered, washed with cold methanol and dried in a
vacuum. Yield: 87%.
2.3. Synthesis of [Cu(qbtz)(PPh3)Br] (1)
To a solution of CuBr (7.2 mg, 0.05 mmol) in acetonitrile (10 mL) was added a solution of
the ligand (13.1 mg, 0.05 mmol) in acetonitrile (10 mL). To this yellow solution a solution of
PPh3 (13.1 mg, 0.05 mmol) in acetonitrile (10mL) was then added dropwise. The final red
solution was left undisturbed and red crystals suitable for X-ray crystallography were obtained
by slow evaporation of the solvent after two weeks. The crystals were filtered off, washed with
cold methanol and dried in a vacuum. Yield: 70%. Anal. Calc. for C34H25BrCuN2PS: C, 61.13;
H, 3.77; N, 4.19. Found: C, 59.85; H, 3.82; N, 4.39%. FT-IR: (KBr, cm-1) νmax: 1589
(C=Nbenzothiazole), 1510 (C=Nquinoline). UV-Vis: λ
(nm) (ε, L mol-1 cm-1) (chloroform): 338
max
(27860), 470 (1126). 1H-NMR: (CDCl3, 400 MHz) δ: 8.63 (d, J = 8 Hz, 1Hj), 8.32 (d, J = 8.4 Hz,
1Hi), 8.20 (d, J = 6.4 Hz, 1He), 8.09 (d, J = 8.4 Hz, 1Hh), 7.93 (d, J = 9.2 Hz, 1Hd), 7.82 (d, J = 8
Hz, 1Ha), 7.64 (t, J = 6.8 Hz, 1Hg), 7.56 (t, J = 7.2 Hz, 1Hb), 7.52-7.20 (Hf,c, PPh3, 17H).
2.4. Synthesis of the [Cu(qbtz)(PPh3)I] (2)
This compound was synthesized by a procedure similar to that used for compound 1 except
that CuI (9.5 mg, 0.05 mmol) in acetonitrile (10 mL) was used instead of CuBr. Anal. Calc. for
C34H25ICuN2PS: C, 57.11; H, 3.52; N, 3.92. Found: C, 57.10; H, 3.37; N, 3.96%. FT-IR (KBr,
cm-1) νmax: 1589 (C=Nbenzothiazole), 1510 (C=Nquinoline). UV-Vis: λ
(nm) (ε, L mol-1 cm-1)
max
(chloroform): 332 (26590), 464 (954). 1H-NMR: (CDCl3, 400 MHz) δ: 8.53 (d, J = 5.2 Hz, 1Hj),
8.33 (d, J = 8.4 Hz, 1Hi), 8.24 (d, J = 7.6 Hz, 1He), 7.97 (d, J = 8 Hz, 1Hh), 7.85 (d, J = 8.4 Hz,
1Hd), 7.70 (t, J = 7.2 Hz, 1Hg), 7.59 (t, J = 7.6 Hz, 1Hb),7.57-7.20 (Ha,f,c, PPh3, 18H).
4

2.5. X-ray crystallography
Single crystal X-ray diffraction data were collected at 298 K with graphite-monochromated
Mo Kα radiation (λ = 0.71073 Å) utilizing a STOE IPDS-II image plate instrument for complex
1, and a Bruker CCD platform diffractometer for 2 at 150 K. Cell refinement, data reduction and
absorption corrections were performed with the help of the program X-AREA (Stoe&Cie, 2005)
[30] for 1 and the programs SAINT and SADABS for 2 [31]. The structures were solved by
direct methods and refined on F2 using the program SHELXL-97 [33]. All non-H atoms were
refined anisotropically. The H atoms were constrained to idealized geometries and Uiso(H) =
1.2×Ueq of the corresponding carrier C atoms. Both crystal structures 1 and 2 showed an
orientation disorder of the 2-(2-quinolyl)benzothiazole ligand, by which the quinoline and
benzothiazole fragments partly switch positions and simulate 2,2'-biquinolyl. This disorder was
taken into account by introducing partly occupied positions for sulfur (S1A, S1B) in the
benzothiazole fragment and the 3- and 4-carbon atoms of the quinoline fragment (C7A, C7B,
C8A, C8B) applying stabilizing EADP and DFIX restraints for them in case of 2, whereas for 1
only DELU restraints were needed. All other atoms of the qbtz ligand in its both orientations
showed an unresolvable superposition and were refined as fully occupied N, C, H single sites
that represent the averages of the benzothiazole and quinoline moieties. The refined population
parameters for the two qbtz orientations were 0.73(1)/0.27(1) in 1 and 0.66(1)/0.34(1) in 2. The
crystallographic and refinement data are summarized in Table 1 and selected bond lengths and
bond angles are shown in Table 2. As is evident from the unit cell dimensions (Table 1), 1 and 2
are not isostructural and the two complexes show clear differences in conformation concerning
the orientation of the PPh3 group and its phenyl rings. It should be mentioned that among the
5

crystals of compound 1 a second polymorph was observed that showed triclinic symmetry, a
lower density, and more disorder than the first polymorph reported above.
Table 1
Crystallographic parameters, data collection and refinement details for 1 and 2.
Empirical Formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
C34H25BrCuN2PS (1)
668.04
298(2)
triclinic
Pī
C34H25ICuN2PS (2)
715.03
150(2)
triclinic
Pī
9.770(2)
9.190(4)
10.979(3)
14.228(3)
103.348(5)
90.959(5)
99.536(4)
1462.1(6)
2
9.172(4)
b (Å)
c (Å)
α (°)
β (°)
18.832(9)
100.433(6)
90.754(6)
108.539(6)
1475.9(12)
2
γ (°)
V (Å3)
Z
Dcalc (Mg/m3)
1.517
2.266
1.609
1.938
µ (mm-1)
Crystal size (mm)
F(000)
0.36 × 0.26 × 0.17
676
0.3 × 0.1 × 0.07
712
2.61-26.00
multi scan
13237
1.10-26.45
multi scan
11166
θ range (°)
Absorption correction
Reflections collected
Rint
0.0687
0.0253
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I> 2σ(I)](a)
5758/134/389
0.955
5739/6/373
1.028
R1= 0.0298,wR2 = 0.0729
0.83 and -0.63
R1 = 0.0411, wR2 = 0.0962
0.63 and -0.45
Largest diff. peak and hole (e Å-3)
R1 = ∑||Fo|-|Fc||/ ∑|Fo|, wR2 = {∑[w(Fo -Fc2)2]/ ∑[w(Fo ) ]}1/2
(a)
2
2 2
2.6. Antibacterial activity
The antibacterial activities of the ligand and its complexes were tested by the well-known
diffusion method using Sabouraud dextrose agar and Müller Hinton agar [35]. The zone of
inhibition (MIZ) was recorded upon completion of the incubation and the mean diameter for
each complex at 100 µg mL-1 was recorded. Stock solutions of 1 and 2 were prepared in
6

dimethylsulfoxide. The MIZs produced by the compounds were compared with the standard
antibiotic Penicillin of a similar concentration. Each test was carried out three times to minimize
any error. In order to clarify the effect of DMSO in the biological screening, blank studies were
carried out, and no activity was observed against any bacterial strains in pure DMSO.
3. Results and discussion
3.1. Synthesis
The unsymmetrical bidentate ligand qbtz was prepared from 2-aminothiophenol and quinaldic
acid by an efficient and benign method recently developed in our laboratory, using
triphenylphosphite (TPP) in the presence of the inexpensive ionic liquid tetrabutylammonium
bromide (TBAB) as the reaction medium [28]. The product was precipitated by the treatment of
the final viscous slurry with methanol. This remarkably simple workup procedure gave the pure
benzothiazole product in high yield (87%) after a short reaction time (15 min), without the need
for further purification by column chromatography.
It is well known that amides are commonly formed via the reactions of carboxylic acids with
amines. Formation of amides has also been documented in our previous work on the synthesis of
related compounds [36-38]. The thiol group could in turn attack the CO group to give the
cyclization product. The mechanism, as shown in Scheme 1, was assumed to be operative.
Scheme 1. Proposed reaction mechanism for the synthesis of 2-(2-quinolyl)benzothiazol, qbtz.
7

The two copper complexes 1 and 2 were synthesized by the reaction of qbtz with the
corresponding copper(I) halide in acetonitrile in the presence of the ancillary ligand PPh3. Both
complexes are stable in air, solution and in the solid state.
3.2. Description of the crystal structures 1 and 2
The molecular structures of complexes 1 and 2, with the atom numbering scheme, are
presented in Figs. 1 and 2 and selected bond angles and distances are listed in Table 2. Both
complexes crystallize in the triclinic space group Pī, but they are not isostructural in terms of
their crystal lattices. While a tetrahedral geometry might be expected for a four coordinated
copper(I) center, the coordination sphere around the copper atom in 1 and 2 is distorted by the
restricting bite angle of the chelating ligand. The copper(I) ion in these complex is in a
pseudotetrahedral environment, with large angular distortion arising from the low intraligand
N1-Cu1-N2 chelate angle (77.90(12)° in 1 and 79.06(11)° in 2), that is much less than the ideal
value of 109.5°. On the contrary, the angles N1-Cu1-P1 (119.40(8)° in 1, 110.87(7)° in 2) and
N2-Cu1-P1 (125.05(8)° in 1, 121.01(7)° in 2) are much larger than those of an ideal tetrahedron.
The bond distances Cu1─N1 (2.131(3) Å in 1 and 2) and Cu1─N2 (2.126(3) Å in 1 and
2.084(2) Å in 2) are within the expected range and are in agreement with those reported for a
related complex (2.098(2) and 2.024(2) Å) [39]. The Cu1─P1 bond distance (2.2076(9) Å in 1
and 2.2114(13) Å in 2) is similar to that found in [(Cu(ca2en)(PPh3)(X)] (Cu─P = 2.2036(8) Å
(X = Br) and 2.2327(6) Å (X = I)) [40]. The Cu1─X1 bond lengths of 2.4366(6) Å in 1 and
2.5795(11) Å in 2 agree well with the data reported for the related complexes
[(Cu(ca2en)(PPh3)(Br)] (Cu1─Br1 = 2.4400(5) Ǻ) [40] and [Cu(bpy)(PPh3)(I)], (Cu1─I1 =
2.6469(4) Å) [41].
8

Fig. 1. The ORTEP diagram of [Cu(qbtz)(PPh3)Br] (1). Non-H atoms, represented as
displacement ellipsoids, are plotted at the 30% probability level, while H atoms are shown as
small spheres of arbitrary radius. Only the predominant orientation of the disordered qbtz ligand
is shown.
Fig. 2. The ORTEP diagram of [Cu(qbtz)(PPh3)I] (2). Non-H atoms, represented as displacement
ellipsoids, are plotted at the 30% probability level, while H atoms are shown as small spheres of
arbitrary radius. Only the predominant orientation of the disordered qbtz ligand is shown.
9

Table 2
Selected bond lengths (Å) and angles (°) for 1 and 2.
Complex
Bond lengths
Cu1-X1
Cu1-N2
Cu1-N1
C34H25BrCuN2PS (1)
C34H25ICuN2PS (2)
2.4366(6)
2.126(3)
2.131(3)
2.2076(9)
2.5795(11)
2.084(2)
2.131(3)
Cu1-P1
2.2114(13)
Bond angles
N2-Cu1-N1
N2-Cu1-P1
N1-Cu1-P1
N2-Cu1-X1
N1-Cu1-X1
P1-Cu1-X1
77.90(12)
125.05(8)
119.40(8)
101.02(7)
99.77(8)
79.06(11)
121.01(7)
110.87(7)
112.43(7)
112.67(7)
115.29(3)
123.08(3)
3.3. Spectral characterization
The FT-IR data of the copper complexes are listed in Section 2. The IR spectrum of the free
ligand shows two bands at 1558 and 1593 cm-1, characteristic of C=Nquinoline and C=Nbenzothiazole
stretching vibrations [28,42]. The ν(C=N) band is generally shifted to lower frequencies in
copper complexes relative to the free ligand, indicating a decrease in the C=N bond order due to
back bonding from the Cu(I) ion to the π* orbital of the ligand and increasing the resonance in
the more planar coordinated benzothiazole ligand. The C=Nquinoline and C=Nbenzothiazole stretching
vibrations appear at 1510 and 1589 cm-1 respectively in the IR spectra of the copper complexes.
The UV-Vis spectra of these compounds were obtained in chloroform solution. The copper(I)
ion, with a d10 configuration, is diamagnetic and no d-d electronic transition is expected for its
complexes. However MLCT and intraligand transitions are expected [39]. These two transitions
appear at 470 nm (ε = 1126 mol-1 L cm-1) and 338 nm (ε = 27860 mol-1 L cm-1) for complex 1
and at 464 nm (ε = 954 mol-1 L cm-1) and 332 nm (ε = 26590 mol-1 L cm-1) for complex 2. There
is only one intraligand transition at 332 nm (ε = 27100 mol-1 L cm-1) in the UV-Vis spectrum of
10

the ligand. The lower energy of the MLCT absorption band in the bromo complex relative to the
iodo complex is in accord with the higher σ-donor ability of the bromide ligand as compared to
that of the iodide ligand, rendering the central Cu(I) ion more electron rich in the bromo
complex.
1
In the H NMR spectrum of the free ligand the ten aromatic protons appear as six doublets
(Hj,i,e,h,d,a) and four triplets (Hg,b,f,c) [28]. Similar features are expected in the 1H NMR spectra of
the two copper(I) complexes, with some shift to lower fields indicating the coordination of the
qbtz ligand to the Cu center. However, in complex 1, the six doublets due to Hj,i,e,h,d,a and two of
the triplets (Hg,b) appear as separate peaks, while the two other triplets (Hf,c) overlap with the
fifteen proton signals of the coordinated PPh3 ligand. In complex 2, one of the doublets and two
of the triplets (Ha,c,f) overlap with the PPh3 signals. The signal due to Hj, for example, appears at
8.52 ppm in the spectrum of the free ligand, while it appears at 8.63 and 8.53 in the spectra of the
bromo and iodo complexes respectively.
Scheme 2. Chemical formula of the ligand qbtz.
3.4. Antibacterial activity
The antibacterial activity of the ligand qbtz and its copper complexes 1 and 2 was tested
against Gram- positive and Gram-negative bacteria in DMSO solution. The diameters of the zone
of inhibition produced by the compounds were compared with standard samples having the
antibiotic penicillin of a similar concentration. The screening results are summarized in Table 3.
It is evident that the two complexes are in general more active than the free ligand. Moreover, of
11

the two complexes, [Cu(qbtz)(PPh3)Br] is more effective against Salmonella typhi and
[Cu(qbtz)(PPh3)I] shows higher activity against Staphylococcus aureus. In the metal complexes,
the polarity of the metal ion is presumably reduced to a greater extent and the increased
delocalisation of π electrons over the whole chelate ring enhances the lipophilicity of the
complex. This in turn enhances the penetration of complexes into the lipid membrane of the
microorganisms. Interestingly, both complexes 1 (MZI = 24) and 2 (MZI = 20) exhibit an
antibacterial activity against Salmonella typhi higher than that observed for penicillin (MZI = 18).
Table 3.
MIZ (mm) for the antibacterial activity of the qbtz ligand and its Cu(I) complexes 1 and 2.
Staphylococcus aureus Bacillus cereus
Salmonella typhi
Bacteria
Ligand (qbtz)
[Cu(qbtz)(PPh3)Br]
[Cu(qbtz)(PPh3)I]
Penicillin
18
14
21
14
19
15
15
24
20
20
33
18
DMSO
None
None
None
3.5. Electrochemical studies
The electrochemical behavior of the qtbz ligand and its corresponding complexes has been
studied by cyclic voltammetry in DMF solution with 0.1 M [N(n-Bu)4]PF6 as the supporting
electrolyte at a glassy carbon working electrode. The approximate concentrations of the
compounds were 1×10-3-10-5 M. Ferrocene (Fc) was used as an internal standard and all redox
potentials are referenced to the Fc+/0 couple [29].
The electrochemistry of the qtbz ligand in DMF solution shows two redox processes at -1.68
and -2.20V (Fig. 3). As reported in our previous studies, these reductions are attributed to the
quinoline and pyridine rings and are shifted to more positive values in the corresponding Cu(I)
complexes due to the transfer of electron density to the metal center [43-46].
12

Fig. 3. Cyclic voltammogram of the qtbz ligand in DMF at 298 K, scan rate = 100 mV s-1, c =
2.2 × 10-3 M.
The electrochemical properties of the copper complexes were investigated in DMF solution at
a scan rate of 100 mV s-1 and the voltammogram of [Cu(qtbz)(PPh3)Br] is shown in Fig. 4 as a
representative example. The cyclic voltammograms of the complexes display three oxidative
responses in the potential range 0.0-0.8 V. The anodic wave observed at 0.22 V, with the
corresponding cathodic wave at 0.02 V, is attributed to the CuI/II couple, which is in agreement
with similar reports on Cu(I) complexes [47-50]. The two quasi-reversible anodic processes
observed at 0.62 and 0.73 V are due to the oxidation of the benzene rings of triphenylphosphine
and the Br- anion [48,50].
Upon scanning cathodically, three reduction waves are observed in the potential range -0.7 to
-1.6 V. The reductive response at -0.71 V, (Fig. 4) is suggested to be mainly metal centered and
is due to the CuI/0 redox process [48]. The oxidative response of this process, corresponding to
Cu0/I, is observed at 0.06 V.
13

Fig. 4. Cyclic voltammogram of [CuI(qtbz)(PPh3)Br] (1) in DMF at 298 K, scan rate = 100 mV
s-1, c = 3.6 × 10-4 M.
The final reduction couples at -1.27 and -1.54 V are ligand centered and correspond to the
reductions of the quinoline and pyridine rings of the coordinated qtbz ligand. These reductions
were also observed in the cyclic voltammogram of the free ligand and are shifted to more
positive values in the corresponding complexes (Fig. 4) [44, 46].
The cyclic voltammogram of [Cu(qtbz)(PPh3)I] shows features similar to those observed for
[Cu(qtbz)(PPh3)Br], with an anodic shift in the peak position corresponding to the CuI/II
oxidation (0.36 V), resulting from the weaker σ-donor ability of the I- ligand relative to the Br-
ligand in the corresponding copper complexes. This observation conforms to the relative
energies of the MLCT absorption bands in the electronic spectra of the two complexes (vide
supra).
14

4. Conclusion
This paper describes the synthesis of two new copper(I) complexes of the bidentate ligand 2-
(2-quinolyl)benzothiazole. The crystallographic characterization of these complexes shows a
distorted tetrahedral geometry around the copper centers. Both complexes are stable in solution
and in the solid state, and cyclic voltammograms of the two complexes in DMF display a
CuI/CuII electrochemically irreversible process. Antibacterial tests showed that both complexes
possess biological activity and exhibit antibacterial activity against Staphylococcus aureus and
Salmonella typhi comparable to that observed for the standard antibiotic penicillin.
Acknowledgements
Partial support of this work by the Research Council of the Isfahan University of Technology
is gratefully acknowledged. Special thanks are due to Professor Kurt Mereiter of the Faculty of
Chemistry, Vienna University of Technology for his generous technical support and to Dr.
Farzaneh Fadaei of the Laboratory of Crystallography, EPFL, Switzerland for helpful
discussions.
Appendix A. Supplementary data
CCDC 1012215 and 1012216 contains the supplementary crystallographic data for 1 and 2.
These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html,
or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found in the online version.
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19

Synthesis, characterization and X-ray crystal structure of copper (I)
complexes of the 2-(2-quinolyl)benzothiazole ligand. electrochemical
and antibacterial studies
Soraia Meghdadi, Mehdi Amirnasr, Afsaneh Mirhashemi, Ahmad Amiri
Two new copper(I) complexes, [Cu(qbtz)(PPh3)(X)] {qbtz = 2-(quinolinyl) benzothiazole and X
= Br, I}, have been synthesized and fully characterized. The X-ray crystal structures of these
complexes have been determined. Cyclic voltammetric behavior and preliminary antibacterial
activity of the ligand and both complexes against Gram-positive and Gram-negative bacteria are
reported.
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